Apparatus and method for use in color reproduction



July 17, 1951 N. R. GUNDERSON ARPARATUS AND METHOD FOR USE IN COLORREPRODUCTION 6 Sheets-Sheet 1 'Filed OCL. 9, 1946 Mmm/v R. uNDL-Rso/v,

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my W7 1951 N. R. GUNDERSON APPARATUS 'AND METHOD FOR USE IN COLORREPRODUCTION Filed OCL. 9, 1946 6 Sheets-Sheet 2 N. R. GUNDERSON July17, 1951 APPARATUS AND METHOD FOR USE IN COLOR REPRODUCTION- Filed OCT..9, 1946 6 Sheets-Sheet 3 mwN..

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vim' July 17, 1951 N. R. GUNDERSOM 2,560,567

APPARATUS AND METHOD FOR USE TN COLOR REPRODUCTION Filed Oct. 9, 1946 6Sheets-Sheet 5 500 600 fig. 12.

`uly 17, 1951 N. R. GUNDERSON 2,560,567

APPARATUS AND METHOD FOR UsE 1N COLOR REPRODUCTION AFiled Oct. 9, 1946@Sheets-Sheet 6 lig 9.

' NORMA/VR, uA/QERSON, INV/5N ToR.

Patented July 17, 12951 UNHTED STATES PAT ENT Oi? HQE Norman Et.Gunderson, Pasadena, Calif'.

Application ctcber 9, 1946, Serial No. '702,173

(Cl. ri- 5.2)

14 Claims. l.

The present invention relates generally to a device, apparatus, systemand methods particularly adapted for use in the rapid, economical andaccurate reproduction of photographs, colored transparencies, maps orother pictorial representations, the reproductions being either in theform of prints or facsimiles for observation by reflected light or inthe -form of photographic color separation images, from which printingplates may be made for use in printing colored reproductions oracsimiles. These reproductions may be of the same or different size thanthe original and either in monochrome or in substantially natural color.

The invention is adapted to Wire or wireless transmission of pictorialrepresentations and permits colored prints or reproductions to be sentby Wire or wireless with an accuracy and denition which has not beenapproached even by existing monochrome methods. More particularly, thepresent invention relates to a device, apparatus, system and methodadapted to scan an original colored subject or pictorial representationor photographic color separation images thereof and to apply variouscolored inks and a black ink upon a suitable medium, such as paper orthe like, for reproducing a true colored pictorial representation,facsimile or reproduction of the original colored subject. Also, theinvention contemplates scanning an original colored sub-ject, apictorial l.

representation or photographic color separation images thereof, andmaking a pluralityl of corrected color or chromatic photographicseparation images and a black or achromatic photographic separationimage, the various corrected color separation images being'adapted foruse in` making a plurality of corrected color printingv plates, or thelike, and the black separation image being adapted for use in making ablack printing plate, or the like.

The various corrected color printing plates are adapted to printcorrespondingly colored inks, or the like, and the corrected blackprinting plate is adapted to print black ink, or vthe like, forreproducing in color a true pictorial representation, facsimile orcolored reproduction of' a colored subject.

The particular forms 4,of theinvention described and illustratedherein,4 in the embodiments of this invention adapted to make coloredpictorial representations or facsimiles, contemplate utilising threedistinct color channelinputs which are modiiied into three distinctcolor channel outputs and a black channel output. In the' embodimentsofy this invention adapted for making corrected photographic colorseparation images andi a black photographic separation image, three`color channel inputs are also modified into three color channel outputsand a black channel output which are utilized in making thecorresponding separation photographic images.

Both of these above mentioned color reproduction processes are of thetype generally known in. However, this, invention is not limited to saidfour color process;

the art as a four color process.

or to the exact forms described herein. Although the various elementsdescribed in Adetail hereinafter have been correlated to an integratedsystem described to the above defined fields of endeavor, it is to beunderstood that many of such elements are individually noveland of greatutility in many arts and uses removed from the specie field of endeavorto which these elementsv have been applied by me as disclosed herein.

The present application is a continuation-inpart of my application,Serial No. 426,220, filedY January 9, 1942, now Patent No. 2,413,706.Said` patent application includes the broad idea of` photoelectricallyscanning three photographicV color separation images which have beenmadethrough suitable lters or the like, or other means for directingvarious spectral components to thel the three color channels are thenInodiedin the' mixer. First, an equal value or grey voltage issubtracted,

from the signal in each color channel in orderto Second, the signal ineach,

This modification consists of four.` steps.

take out the black. color channel is changed by the addition or sub.

traction of a portion of the signal in each of the;F

other two color-channels. This step is done in order to correct for theoverlapping spectral ab:-

sorption characteristics of the reproducing col-` ored inks. The Athirdstep is the selection of the color channel having the minimum response,that;

is,v the channel corresponding to the minimum coverageA of colored ink.Fourth, uthis minimum: value or signal is used in regulating the valueof theigrey voltage'which was previously subtracted from allthree inputcolor signals in an inverseA feedback manner soxthat the valueof thesignal for the minimum selected color channel isregulatedto anessentially constant value correspondingto essentially zero coverage ofthe correspondingcolored ink. This has the effect of causing.`

only the two color channels having the electric outputs corresponding tothe greatest colored ink coverages to be effective at any one instant,the third instantaneously minimum output color channel being ineffectiveand causing no colored ink coverage for that channel.

The grey voltage mentioned above is utilized in generating or creating afourth or black achromatic output signal in a black output channel.

The electric outputs of the various color channels and the electricoutput of the black channel are used for controlling suitablereproducing head means adapted to atomize, mix and spray the variouscolored inks and the black ink upon a suitable medium such as paper orthe like in accordance with the three color output signals and the blackoutput signal, thus making a color reproduction of the colored original.

This continuation-in-part of the before mentioned parent applicationembodies improvements over and above the parent application which adaptsthe invention to making theoretically correct colored pictorialrepresentations, facsimiles or reproductions of the colored subject orfor making correct photographic color separation images and a correctblack separation photographic image adapted to make correspondingprinting plates adapted to print correspondingly colored inks for makinga true colored pictorial representation, facsimile or reproduction ofthe original colored subject.

It should, perhaps, be explained at this point that the reproducing headin the parent application above referred to, applies inks of the variouscolors and black ink upon a suitable surface in linear relation to theinput signals to the reproducing head. Thus the density of the coverageof any or all of the various colored inks or the black ink is variedvirtually linearly with respect to the signals received by thereproducing head from the color channels and the 4black channel, andsince the color channel signals received by the reproducing head arelogarithmic with respect to the light received by the photoelectricscanning means associated with each color channel, and since lightreceived from the colored reproduction or facsimile made by spraying thecolored inks and the black ink upon a suitable surface, isantilogarithmic or exponential with respect to the density of the inksforming the color reproductions, the light reflected from the colorreproductions will have a linear relation to the light input to thephotoelectric scanning means.

However, it has been found that if the above mentioned system is to beused in making three correct chromatic color separation photographicimages and a correct black separation photographic image, theantilogarithm of the output signals in the color channels and the blackchannel should be preferably taken and used for controlling four linearlight valves adapted to cooperate with four photosensitive lms or thelike, which may be mounted upon a rotating drum or the like for makingfour correct separation photographic images, three of which are colorseparation photographic images and the fourth of which is a blackphotographic separation image, and which may be used for making halftoneprinting plates or the like, in a manner well known in the art formaking true color reproductions or facsimiles of a colored subject.

The extra step of taking the antilogarithm of the output signals of thecolor channels and the black channel when making the correct colorseparation photographic images and a correct black separationphotographic image, as above described, is desirable because of the factthat within the normal exposure range of the film the density of aphotographic image formed on a photographic film or the like, isvirtually proportional to the logarithm of the light intensity exposingthe film and the input signals to the light valves, whereas in thearrangements in the parent application the various colored inks and theblack ink are sprayed on paper directly by the reproducing head forvarying the density of the various colored ink coverages and the blackink coverage linearly with respect to the input signals to thereproducing head.

The present continuation-in-part includes means and methods forobtaining theoretically correct color reproduction. I have found that iftrue color reproduction is to be achieved and is to be based upon theuse of three given real primary colors, the receptor for each color (areceptor being a material or device which undergoes some change whensubjected to radiant energy in the form of light, and thus, may serve torecord or indicate the amount of light it receives) must have a spectralsensitivity versus wave length curve which is negative in certainspectral regions. This is caused by a reason of the fact that nocombination of three real primary colors can match spectrum colorsunless negative values of at least one of the real primary colors areused, because spectrum colors are of a much deeper hue than any realcolors obtainable. Therefore, perfect color reproduction requires thatthe receptors for the various colored channels under one of the generalsystems illustrated herein, comprise three pairs of photographic colorseparation photographic images which have been made through suitablefilters having the desired spectral sensitivity, so arranged that onephotographic separation image of each pair contains the positive portionof the spectral sensitivity versus wave length curve of the receptor andthe other colored separation photographic image contains the mirrorimage of the negative portion of the spectral sensitivity versus wavelength curve of that receptor which is adapted to be subtracted from theother curve. In other words, each color channel has two photographiccolor separation images and two photoelectric cells adapted to scan saidimages. These, together with the filters or the like, through which theimages have been made, comprise a receptor.

There are three such receptors, each receptor in combination having thedesired spectral sensitivity versus wave length curve, including bothpositive and negative values in different spectral regions.

The method used in determining the spectral sensitivity characteristicsof the three receptors, is to first determine the trichromaticcoefficients of the three real primaries to be used in colorreproduction, :cfg/rer, gygzg, :cbybzb (Hardys Handbook of Colorimetry,pages 9-13). The required spectral sensitivity versus wave lengthcharacteristics of the three receptors in then determined by thefollowing set of linear equations:

rsr+gsg+xbsb= yrSr+ysSs+ybSb=y ZrSr+2gSg+ZbSb=E where Sr, Sg and Sb arethe desired spectral sensitivities of the three receptors and and a arethe basic data concerning the chromatic properties of the human eye suchas those publishedby -the International Commission on Illumination.

' Another means and method for achieving theoreticallycorrect colorreproduction similar to that described above, utilizes only three colorseparation positives, one for each color channel. 'Ihe three colorseparation positives are made through suitable lters such that thespectral sensiti-vityfof the three receptors corresponds to threeimaginary primaries not obtainable in reality. Since three imaginaryprimaries are used, no negative values of the spectral sensitivityversus wave length `curve for each receptor are needed. The threeimaginary primaries used in calculating the desired spectral sensitivityversus Wave length of the three receptors might, for example, be thethree imaginary primary colors standardized by the InternationalCommission -on Illumination (see page 'l of Hardys Handbook ofColorimetry) or various other imaginary primaries might be used. Thethree signals in the three color channels corresponding to the threeimaginary primaries are color transformed by color transformer means tothree -new electric signals corresponding to three real, primary colors.This transformation is-according to the following linear transformationequations:

where r,'g and b are the tristimulus values of the original imaginaryprimaries and r', g and b' are the ltris'ilimulus values of the new setof real primaries, and k1 to kg are the tristimulus values of theoriginal primaries on the basis of new primaries. (See page '1, HardysHandbook of Colorimetryf) This continuation in part also contemplatesthe use of alternate apparatus and methods for converting three colorlinput signals'iinto four output channels including three color channelsand a black channel.

At any given instant not more than two of the color output channels areeffective and the black channel is also efective since a mixer similarlymultiplies the three color input signals so as to cause the color outputsignal corresponding to the least colored inl; coverage to be maintainedat a preselected, xed value, corresponding to no colored ink coveragefor that channel. The black or achromatic channel has an output signalwhich is a vfunction of the multiplication necessary tochange saidminimum output channel to a value corresponding to no ink coverage forthat channel.

It can 'readily be seen that this modifying or mixing-effect is inactuality an equal multiplying or -dividing action of all of the coloroutputs. Mathematically, adding or subtracting the logarithm of a firstquantity to or from the logarithm of -a second quantity and then takingthe antilogarithm thereof, corresponds to directly multiplying ordividing the second quantity by thefrst quantity. It is possible to usea system where logarithme are taken of the three color signals and thethree logarithmic color signals added to or subtracted from so as tocause one of said logarithmic signals corresponding to the least ink tobe-maintained at a xed, preselected value corresponding to no coloredink coverage for that channel, and then taking the antilogarithm of thethree modiied logarithm-ic color channels as the three final coloroutputs. The antilogarithm of the quantity added to or subtracted Vfromthe secarse-v three color signals may be used as the final blackoutput,the four outputs being adapted to control four linear light valves formaking three corrected color separation photo-graphic images and afourth black or achromatic corrected separation photographic image orthe four logarithmic output signals may go directly to a reproducinghead means for directly applying the various inks for making a coloredpictorial representation.

In a similar manner the three color signals may be multiplied or divideddirectly so as to maintain the color signal corresponding at a giveninstant to the least colored ink coverage, at a preselected, iixed valuecorresponding to no colored ink coverage for that channel. Saidmultiplying factor used in equally multiplying the three color signalsmay then be used for creating the black or achrornatic output signal.

The four separation photographic images may be made with four linearlight valves controlled by the four output signals in the mannerhereinafter described or the logarithms of the signals may be taken forcontrolling a reproducing head tor making colored pictorialrepresentations by the direct application of ink as hereinbeforedescribed.

The reason for converting three color input channels into three coloroutput channels and a black output channel is as follows:

It has been found by the printing trade that while theoretically perfectcolor repro duction may be achieved by the use of various colored inksalone, in practice this is not satisfactory. Muddy locking pictureslacking in contrast and definition result from such a three-colorprocess.

In such a three-color process shades of black or gray are formed bycombining the various colored inks in virtually equal proportions. Thisdoes not produce a clear, sharply outlined, defini- "re black. It is,therefore, desirable that the varying density and all shades of blackand gray oi a color reproduction be achieved by use of a black ink.

A black inl: may be considered to be composed of or equivalent to acombination of equal percent coverages of each of three theoreticallyperfeet colored inks. Such theoretically perfect colored inks may bedeiined as a set of colored inks each of which absorbs light completelyin one and only one of the color bands, red, green and blue. These colorabsorption bands may not overlap nor may there be gaps between them inthe absorption curve. Such inks are not available. It is thereforetheoretically possible and from the standpoint of making colorcorrections highly desirable to use an amount of black inlc suiiicientto reduce the coverage of the colored inl; correspending to the leastcoverage to zero or essentially zero. In other words, at any one pointthe ink coverage should consists entirely cf a black inl: and twocolored inks, the black ink coverage being just suiilcient to havereduced the least colored inl; coverage to zero and to correspondinglyreduce the other tvo colored inks.

It has been found experimentally and it can be shown to have a soundtheoretical basis that the effect of varying the percent coverage oi theblack ink is to multiply the light reected at any wave length by thesame factor. This is true no mattei' what combination of printing inkshave been previously used in printing the paper. A discrepancy to thisrule is found when the percent coverage of the black ink approachesbecause of the small percentage of white light reif-.ected from thesurface of lthe black ink. The effect of the black ink is equivalent tothat of a shutter on the light source for the spot in question.Therefore, it is necessary that means be provided for moditying thethree color inputs into three color out- Iputs and a black output in amanner which multiplies or divides all of the color channel outputs bythe same factor so as to cause the color output instantaneouslycorresponding to the least colored ink coverage to be maintained at thepreselected xed value corresponding to no colored ink coverage. Theamount of said multiplication needed determines the black output. In theforms of this invention adapted to directly controlling the applicationof ink to a suitable medium through a reproducing head or the like, thesituation is mathematically the same except that the three color channeloutputs and the black output must be in the logarithmic form whenapplied to said reproducing head if the correct color reproduction is tobe obtained and the black output is equal to an amount which has beeneffectively added to or subtracted from the color signals so as to causethe color output signal, corresponding to the least colored inkcoverage, to be virtually maintained at a value corresponding to nocolored ink coverage.

In a color reproduction process two colored inks are printed upon thesame surface, the amount of light reflected by the paper and passingthrough one colored ink will be modified by the amount of anothercolored ink superimposed thereon. This is caused by reason of the factthat no really pure colored inks may be obtained. All colored inksobtainable have overlapping color absorption characteristics. In otherwords, they both absorb light in a certain spectral region common toboth; thus, for example, if a certain amount ci yellow (or blueabsorbing) ink is printed upon a suitable surface and then a certainamount of magenta ink is superimposed thereon, the amount of lightreflected from the paper in the blue spectral region will be much lessthan normally would occur with the same yellow ink coverage and nomagenta ink superimposed thereon. It may be shown that in a halftoneprinting process wherein dots placed at various angles print the variouscolored inks, the amount of two colored inks which will be superimposedis a function of the percentage of coverage of one ink multiplied by thepercentage of coverage of the other ink.

In the forms of my invention adapted to reproduce a colored pictorialrepresentation or facsimile by means of the hereinbefore mentionedreproducing means adaptedto atomize, mix and spray the various inksdirectly upon a suitable medium such as paper or the like, the variouscolored inks are atomized and mixed in the air stream which depositsthem upon the paper. Therefore, the modication of the amount of lightreflected from the paper in a spectral region corresponding to a givencolored printing ink when combined with a certain amount of a secondgiven colored printing ink is a function of the amount of the two inksused, different from the similar function in the above mentionedhalftone printing process.

In the above described systems wherein three color inputs are modied soas to have four output channels, including three color output channelsand a black or achromatic output channel, an additional color correctingstep may be used for further modifying the signals in the various colorchannels according to the combinations of the various colored inks whichwill be printed so as to virtually compensate for the above mentionedoverlapping color absorption characteristics of superimposed or mixedcolored inks.

The electrical transmission and reproduction of pictorial matter innatural colors has not been satisfactorily achieved heretofore, but isreadily and accurately accomplished by means of the present invention.

The methods and devices of the present invention may be used in thereproduction of colored facsimiles, either from lithographie coloredpictorial representations, color separation photo images or an originalcolored subject. It is to be understood that the forms of the inventionwhich include the step of taking the logarithm of the three color inputsignals are capable of reproducing colored prints either from negativesor positives and are capable of reproducing correct color separationphotographic images, which may be either positive or negative, fromeither negatives or positives.

An object of the present invention, therefore, is to disclose andprovide method and means for scanning a plurality of color Separationimages cooperating with three color input channels and translatingsignals in said three color input channels into two instantaneouslyeffective color signals in three color output channels and a blackoutput signal in a black channel, the output signals being adapted tocontrol light valve means for making four color separation photographicimages adapted for use in making color printing plates or the like.

A further object of the present invention, is to disclose and providemethod and means for scanning a plurality of color separation imagesassociated with three color input channels and translating signals insaid three color input channels into two or less instantaneouslyeiTective color signals in three color output channels and a fourthblack output signal in a black channel; correcting the signals in thecolor output channels to compensate for the overlapping color absorptioncharacteristics of superimposed colored printing inks and utilizing theoutputs for controlling light valves for making four photographic colorseparation images for use in making three color printing plates and ablack printing plate.

It is a further object of this invention to disclose and provide methodsand means for scanning an original colored subject, colortransparencies, pictorial representation or color separationphotographic images and to translate the instantaneous signals in colorinput channels into instantaneous signals in a lesser number of coloroutput channels plus a black output signal in a black output channel andcorrecting the signals in the color output channels so as to compensatefor overlapping color absorption characteristics of mixed colored inksto be used in reproducing a facsimile of the original subject.

An object of the present invention, therefore, is to disclose andprovide method and means for scanning a plurality of color separationimages cooperating with three color input channels and translatingsignals in said three color input channels into two or lessinstantaneously effective color signals in three color output channelsand a black output signal in a black channel, the output signals beingadapted to control reproducing head means for applying inks upon asuitable medium such as paper or the like, to make a colored pictorialrepresentation or facsimile.

A further object of the present invention is to disclose and providemethod and means for scanning a plurality Aof color lseparation imagesyassociated with three color input channels and transforming signals .insaid three .color .input channels into ytwo or less linstantaneouslyeffective .color Vsignals in three color foutput 4channels and a'ffourthbiacksignal iin a black .output chantnel; correcting `the 'signals inthecolor Voutput .channels vto ycompensate `for the .overlapping color-absorption characteristics of mixed colored 'printing inks andutilizing the outputs or controlling reproducing head means for:atomizing and spraying colored inks and black ink upon a suitablemedium such vas paper Aor the like, to make .a colored .pictorialArepresentation or facsimile.

Another object of .the .present invention is to disclose and providemethod and means wherelIcy automatic compensation or correction may beobtained ior overlapping color absorption characteristics ofsuperimposed or mixed Vinks .employed in making `colored reproductions.

Another object of the present invention is to disclose and providemethod land means whereby Aa vplurality of color input rsignals areconverted .into asimilar number of output signals including a pluralityof color output signals and a correlated .black output signal.

A further object of the present invention is to disclose improvedmethods and apparatus oi the transmission and reproduction of pictorialrepresentations in color and `for the `making of color .printing plates.

It is va further object of this invention to provide method and meansfor transforming sig-- lnals vcorresponding to imaginary primary 4colorsinto signals corresponding 'to real primary colors.

In general, it is an object of the present invention to disclose andprovide 'an integrated method `and apparatus for rsuccessfully rmakingcolor separation photographic images 'adapted ffor use in making truecolor reproductions or facsimilies of an original colored subject,photograph, transparency, separation images of the like, Aor fordirectly making true color reproductions or facsimilies Vof an yoriginalcolored subject, photograph, transparency, separation images, :or thelike.

These and -other subjects, uses, `modifications :and adaptations of thepresent invention willbecome apparent to those skilled in the art fromthe following detailed description of certain eX- emplary forms of thepresent invention, .it being understood that the invention is notvlimited to the specific arrangements hereinafter described 'and shownin the appended drawings, since numerous variations and modications maybe made (as indicated in part hereinafter) without departing from thespirit and scope oi the present invention` In Yorder to facilitateunderstanding, reference will be had to the appended drawingsillustrative of `certain arrangements, circuits, means and modes oroperation embraced by this .invention and .in such drawings:

lFig. l is a rst diagrammatic .representation of various .elementsemployed in making three correct color separation photographic imagesand a black separation photographic image adapted. for use in making`four color printing plates such as halftone vprinting plates or thelike.

Fig. .2 is a second diagrammatic representation of various elementsemployed in making three correct color separation negatives and `a `1I0black separation negative adapted for 4'use 'in making four printingplates.

Fig. 3 is a third diagrammatic Vrepresentation of various elementsemployed vin making three correct color separation negatives and a blackseparation .negative which may 4be used for 'mak- 4ing four `printingplates.

Fig. 4 is 'a wiring diagram schematically il- -lustrating the additiveor fsubtractive 4mixer of .my invention.

Fig. 5 is a lwiring diagram .schematically il- -lustra'ting the inkcolor absorption corrector of `my invention.

Fig. 6 is a wiring diagram .schematically vLillustrating the multiplyingmixer `ofimy invention.

Fig. '7 is a Wiring diagramschematically .illustrating the colortransformer of my invention.

Fig. y8 is a wiring ydiagram :schematically .illustrating theVcompensator of my invention.

Fig. .9 is a .graph of the spectral .sensitivity versus wave lengthfcurve of "three receptors adaptedfor use in the'system where I utilizethree .imaginary primarycolor inputs.

Fig. -10 is ra chromacity diagram showing 'three imaginary primariesutilized by me in one =form roi 4my invention.

Fig. 11 is a graph :of a theoretically lScor-rect spectral`sensitivity-versus-wave length `cur-ve `of a receptor `corresponding toyone -co'lor channel and .having both positive .and .negative valuesvvas is required vfor correct Vcolor reproduction -and determined by thecolored inks to be used in color reproduction.

Fig. 12 is a graph of .a .practical receptor which lmay readily beachieved in :practice and vwhich has vpositive'values ina given spectralregion.

IFig. 13 is a graph :of spectral sensitivity-versuswave length curve ofa practical receptor having positive values in a :spectral regiondiierent from the receptor shown in Fig. 2 and which also -may readilybe achieved lin practice.

A general arrangement of the various elements -included in oneintegrated, complete system for making from three pairs of colorseparation positives, three corrected lcolor `separation negatives and afourth vcorrected black negative 'for use in making three halitone'color printing plates and a fourth halftone black printing plateadapted to print correspondingly colored inks and a 'black ink for.making true color reproductions or facsimiles of a colored subject isdiagrammatically illustrated in Fig. l. As there shown, the scanning-drum, generally indicated at I, carrying six color separation positives2, 3, Il, 5., '6, and 'I is rotated and axially moved by Ia suitabledrive indicated `generally at 8. Details of construction of the scanningdrum and driving means need not .be illustrated, since such means arelavailable vand are well known in the art.

Positioned within the scanning drum I 'are photoeleotric cells 9, It, :II, I2, I3 and I4 adapted to receive light from sources I5, I6, Il', I8,lI9 Iand 20, respectively. The light sources 'I5 t0 2,0 may be separatelight sources or they may be a single light source with means fordividing the light equally vbetween the photoelectric cells 9 rto M.lThe photoelectric cells 9 and I' are connected as by lines 2l and 22with a differential logarithmic amplifier indicated generally at .23.The 'photoelectric cells II and I2 are connected as :by lines 2li and2-5 to a second differential logarithmic ampli-fier indicated ygenerallyat .26. The yphotoelectric cells Iii and It are connected as by lines 21and 28 to a third differential logarithmic amplier :indicated generally`at 29. 'The lines .2il

1.1 and 22, 24 and 25, and 25 and 21 constitute portions of threeseparate color channels, to which reference will be made hereafter.

The differential logarithmic ampliers 23, 26 and 29 may be supplied withelectric power from an electric power supply not shown. Eachdifferential logarithmic amplifier in connection with its two associatedscanning photocells constitutes a scanning means for one color channel.The preferred form of the scanning photoelectric cells 9 to I4 in theexample shown is an electron multiplier, photo tube of anelectrostatically focused, multi-electrode type, the multiple electrodesbeing connected to various points of a tapped resistance or voltagedivider.

The three scanning means utilized and differential logarithmicampliiiers utilized herein are of the type illustrated, described andclaimed in my copending application, Serial No. 702,172 filed October 9,1946, now Patent No. 2,454,871, granted November 30, 1948, which is alsoa continuationfrom each scanning means is a logarithmic function of thedifference between the values of the light received by the two photocells of each channel being scanned. This is accomplished in an -inversefeedback manner by feeding back an anode signal from each differentiallogarithmic amplifier to a tapped resistor across the multipleelectrodes of the two electron multiplier photo tubes of each channelfor varying the amplification of the photo tubes so as to maintain avirtually constant differential anode output from the two photo tubes ofeach channel. The amount of signal fed back from each logarithmicamplifier necessary to virtually maintain the differential anode outputof the two photo tubes of that color channel at a preselected, fixedvalue is a virtually logarithmic function of the differential output ofthe two photo cells of each color channel because of the characteristicsof the multiple electrode, electrostatically focused, electronmultiplier photo tubes used.

The output leads of the differential logarithmic amplifiers 23, 26 and29 are indicated at 30,

A3| and 32 respectively. These output leads may be directly connected tothe input leads 33, 34 and 35 of an additive and subtractive mixerindicated generally at 35. The additive and subtractive mixer 36 may besupplied with electric power from a suitable electric power supply notshown. In the event it is desired to transmit the outputs so as to causereproduction to take place at a distant point, the outputs 30, 3l and 32of the differential logarthmic amplifiers 23, 26 and 29 may be connectedto one or a plurality of transmitters of any of the types well known inthe art. It is to be Iunderstood that in the event a single transmitteris employed, separate channels or carrier waves may be used fortransmitting each of the color channels. Such transmitters are not shownin Fig. l, since they are available and well known in the art. Separatereceivers may be associated with the input leads 33, 34 and 35 of themixer 36 for receiving the signals transmitted by the threetransmitters. Such receivers are not shown since they are available andwell known in the art.

The mixer 35 is connected to four leads 37, 38, 39 and 49. The leads 3T,38 and 39 constitute the three color channels whereas lead 40 may besaid to represent the black lead from the mixer. The mixer involvesmeans whereby the magnitude of the :black output is controlled inaccordance with a modifying factor which similarly modifies the outputof the three color channels so as to cause the instantaneously minimumcolor channel output to be maintained at a Value virtually correspondingto no colored ink coverage for that channel. Details of the preferredform of mixer are illustrated in Fig. 4 and will be describedhereinafter.

The leads 37, 38, 39 and 4i] from the mixer 36 may then be sent throughsuitable antilogarithmic amplifiers indicated generally at 4I, 42, 43and 44. The four antilogarithmic amplifiers 4I to 44 may be suppliedwith electric power from a suitable electric power supply not shown. Thefour antilogarithmic ampliers 4l to 44 act to take the antilogarithm ofthe input signal received by said antilogarithmic ampliers. Theantilogarithmic amplifiers 4! to 44 are provided with output leads 45,46, 4l and 48 adapted to carry said antilogarithmic signals, Theantilogarithmic amplifiers utilized herein are of the type illustrated,described and claimed in my copending application Serial No. 702,172,nled October 9, 1946, which is a continuation-in-part of the beforementioned parent application. It is sufficient to note here that theantilogarithmic amplifiers are designed to assure that the outputsignals from said amplifiers are virtually antilogarithmic with respectto the input signals to said amplifiers.

The antilogarithmic signals carried by the output leads 45, 45 and 41 ofthe antilogarithmic ampliers 4l, 42 and 43, which constitute portions ofthe three color channels, are connected to ink color absorptioncorrector, indicated generally at 49. The ink color absorption corrector49 may be supplied with electric power from a suitable electric powersupply not shown. The color absorption corrector 49 acts to modify thesignals in the three color channels in accordance with the combinationsof colored inks, thepercentage of coverage of the various colored inksand the color absorption characteristics of the inks which are to 'beprinted simultaneously so as to be superimposed or mixed. Details of thepreferred form of ink color absorption corrector are illustrated in Fig.5 and will be described hereinafter.

The ink color absorption corrector 49 is provided with output leads 59,5I and 52 which constitute portions of the three color channels andwhich are connected to linear light valves indicated generaliy at 53, 54and 55. The output lead 48 of the antilogarithmic amplifier 44constitutes a portion of the black channel and is connected to a blacklinear light valve indicated generally at 59. The three color channellight valves 53, 54 and 55 and the black channel light valve 56 vary thelight coming from light sources 51, 58, 59 and 39 which is focused uponfour photographic ilms or the like, 5l, 62, 63 and 94 which are mountedupon a drum indicated generally at 65 which is rotated and axially movedby a suitable drive indicated generally at 66, for making threecorrected color separation negatives 6|, 62 and 63 and a fourthcorrected black separation negative G4.

The general arrangement diagrammatically illustrated in Fig. l will bedescribed hereinafter in detail for the purpose of describing theconstruction of the various elements embraced in the system, the systembeing particularly adapted as for makinar four "color separa-tionnegatives from sin color separation positives as illustrated. it is to'be understood, however, that by minor `changes and mod-ications whichWil-l 'be obvious to those skilled in the art from the subsequentdetailed description, this invention may ybe einp'loyed in theproduction of more or 'less than lthree color` separation images whichmay or may 'not includ-e a black separation image and which may Ibepositive 'and negative and which Amay bel made ire-m )more or "less thansix color separation 'images which -`may be positives `or negatives, and`which may reflect -or tran-smit light, `and which may loe 'made Ifromthe original or -iroin a single colored transparency, yimage or thelike, which may transmit -or reflect light. The light may be passedthrough a beam splitter or colored iil'ters so as to separate thecolored light into suitable l'bands of Vfrequencies. each band thenaecting a separate scanning cell Aor a portion of the light Vfrom -facolored print may be sent through a suitable iilter to separate scanningcells. Details of these modifications need not be described, since theyhave-been previously shown in general forms in vvarious prior patents,such as Patent No;

1,709,926 and Patent No. 1,814,987

As ybefore mentioned, oi the elements shown in Fig. 1, Athe scanningmeans, differential losarit'himic ampliers `and the lantilogarithmicampli" ers are of the type illustrated, described and claimed incopending application, Serial No. 702,172, Which is a-continuationin-part of the 'bef-ore mentioned parent application,Serial No. 426,220, filed January 9, 1942, new Patent No. 2,413,706,0fwhich this application `is also a continuation-'in-part, and will not bedescribed specica'lly herein. The rest of the elements in the systemwill -be described specically in detail hereinafter.

Additive und subtmctiee mixer A-n electrical schematic Wiring diagram ofthe additive and subtracti-ve mixer of this invention is shown in. Fig.4. The input terminals 6l, 5S land Sli are connected `to the leads 33,34 .and 35 of Fig. l, which in turn are connected itc output leads 3D,3| and 32 coming from the diiierential logarithmic amplifiers 25% and125i. The input terminals 'of the mixer el, and Sii-3 are AconN nectedto the grids "it, li and 'l2 4ci input elec- `tron tubes l and l5,respectively. The anodes l, *'il and lil of the tubes 'ifll `andrespectively, are connected through suitable plate resistances 1lb, Biland 8l -to positive vpower input 'terminals 8i?, "83 and s4. input 4tubefle in the `color channel oon- -nected through `resistance ii-5 shunted'by a conu denser '81E to the grid :3l `oi a selector electron tube 88.The grid il also connected through a 'resistor :Bil to negative Vpowerinput terminal. im. The anode vil! ci the .selector tube Bil isconnected through a plate resistance .32 'to a positive power inputterminal VVThe anode "9| o the selector tube *38 is also connectedthrough .a resistance Elfi shunted by a condenser Yi Lto a grid 552.5 oiari-elec-y tron itube lll. The grid lil is `also :connected through aresistor 9S .to `negative :power input yterminal The cathode itil ci?the selector electron Vtube di: lis 4connected vto negative pori/'erinput terminal Ilii'Jli. The :anode mi vci lthe elecm 4tron 'tube S51 isconnected to :positive power :in- :put terminal fl The-cathode Ii'li olfthe input electron tube in the First `color channel and 'the `cathode9F95 fo'f the input electron itube 'M in 'the second -color channel`.and the cathode lilii of The anode |36 of the the input electron 'tube.li in the third colorchan- -nel Iand the .cathode wl fof an electrontube im! in the black channel and the cathode |39 :of the electron tubeall connected in parel-- lel and are connected through :a resistor fiIl] to a ner-ative'power inputterminal lili. 'Theanode lll of the inputelectron tube Till in the second color channel is connect-ed through a,plate resister se to positive vpower input termi-nal 83. The anode "ilis also connected through a resister M2 shunted by aco-ndenser M3 ltotbagrid fil-i of a selector electron tube fit. The grid iii is alsoconnected through resistor Mii to a negative power input terminal lil.The anode H8 of `the selector electron tube Elle in the sec- A'ond colorlchannel is connected in parallel with the anode Si of 'the selectorelectron ltube its in the rst Ycolor channel and is connected throughthe jplate resister Vto positive power input terminal 93. The cathode ofythe selector electron tube Al i5 -i-n the Asecond lcolor channel. isconnected to negative power input terminal i iil. The lanode i3 oi theinput electron tube ".115 in the third Ycolor channel is connected4through plate resistor Si to positive power 'terminal Bil. Tl-1e anode'le of the electron tube l5 is 1aise 4connected through a resist-or "iEil shouted by a 'condenser l|"2| to lthe grid `of a selector electrontube 1123.

the grid il? is yalso connected tl'irough va resistor to negative powerinput terminal The anode |625 oi the selector Velectron .tube k|23 inthe third color channel is connected in peua'llel with the anode Hi8.ofthe selector electron tube li'in Ithe second color .channel and 'theanode @i of the selector electron tube 88 "in the rst color channel andconnected -through Vplate resistor to Vpositive power input terminal 93.The cathode i2? ci? "the selector electron tube lil/23 'is connected tonegative power input terminal i215. The anode .its of the black .outputelectron. `tube 'iiili is connected. through a plate resistor 13d topositive power input terminal iti. "The grid |32 oi" 'the electron tubei'ii 'is connected 'to .a grid 'biasing potentiorocterand ,powersupply'indicatcd lgenerallyat 533 which is also rconnected'to a negative'terminal Li'Sli.

.current and are .therefore inoperative, the selector tube .haring the.most positive lgrid controls .the

.grid voltage .of the ltube .9T vwhich in v.turn controls the cathodevoltages of .the tubes .15 .and |08.

In actual operation :the system Works -n .ein

.inverse feedback manner as follows: .Assume .that

the grid El of .selector .tube 3.8 in .the rst color channel is the.most Lpositive of .the three grids 6l, 1| id and .L22 of the three.selector .tubes :8.8, |f|51and |23 fof the three color channels.Therefore, the tube :38 ,in .the iirst color-.channel is the only.selector tube in operation. -If the grid flil zof `.the 4input tube'130i the first color channel is made ymore negative, the anode of lthetube 13 and the Agrid lill of 4the :selector :tube .8;3 .are made more:positiv/e. The anode :Bel of the tube 88, vthe .grid :9B of the .tubeTSH and :the .cathodes |09., |201, E65., |i15and IDI! of @the .electron4tubes l 91, |08, 15, 14 and 13, respectively, are all made morenegative. In this way the cathode |04 of the input tube 13 of the firstcolor channel changes in potential almost as much as the originalpotential change of the grid 10. The anode voltage of the tube 13 is atthe same time regulated to a practically constant voltage. This voltageis made to correspond to zero percent coverage of the correspondingcolored ink for that color channel, and the potential of the outputsignal at terminal |35 is such as to result in zero percent coverage ofthe corresponding colored ink for that channel.

The function of the mixer is to add or subtract a voltage to all threeinput signals from the differential logarithmic amplifiers so that thesignal corresponding to the most light and the least colored ink isregulated to constant value. This signal corresponds to the mostpositive anode and the most negative grid of the input tubes 13, 14 and15. Thus, it can be seen that the voltages at the output terminals |35,|36, |31 and |38 correspond to the theoretically correct output voltagesif correct color reproduction is to be obtained as outlinedhereinbefore.

Color output terminals |35, |36 and |31 and the black output terminal|38 of the mixer indicated generally at 36 in Fig. 1 are connected,respectively, to leads 31, 38, 39 and 40 which are connected to theinput terminals of four antilogarithmic amplifiers indicated generallyat 4|, 42, 43 and 44 in the Fig. 1. These antilogarithmic ampliers arenot described in detail since they are illustrated, described andclaimed in my copending application, Serial No. 702,172, filed October9, 1946. Suflice it to say that said antilogarithmic ampliers areadapted to convert four input signals into four output signals virtuallyantilogarithmic with respect to the four input signals.

The black output lead 48 from the black antilogarithmic 44 is connectedto a linear light valve indicated generally at 56 or blackantilogarithmic amplier 44 may be used directly as an antilogarithmicnonlinear light valve in a manner fully illustrated, described andclaimed in my copending application, Serial No. 702,172.

Superimposed ink c0101 absorption corrector The three color output leads45, 46 and 41 from the three color antilogarthmic ampliers 4|, 42 and43, shown in Fig. 1, are connected to input terminals |39, |40 and |4|of a superimposed ink color absorption corrector indicated generally at49 in Fig. l and more specically in electrical schematic form in Fig. 5.

Referring to Fig. 5, the color channel input terminals |39, |40 and |4|are connected to grids |42, |43 and |44 of cathode follower electrontubes |45, |46 and |41, respectively. The anodes |48, |49 and |50 ofcathode follower tubes |45, |46 and |41 are connected to positive powerinput terminals |5|, |52 and |53 respectively. The cathodes |54, |55 and|56 of the cathode follower tubes |45, |46 and |41, respectively, areconnected through cathode resistors |51, |58 and |59 to negative powerinput terminals |60, |6| and |62, respectively. The cathode |54 of thecathode follower tube |45 in the rst color channel is connected througha resistor |63 to the grid |64 of a selector electron tube |65. The grid|64 is also connected through a resistor |66 to negative power inputterminal |61. The anode |68 of the selector tube |65 is connected topositive power input terminal |69. The cathode of the selector tube |65is connected through a cathode resistor |1| to negative power inputterminal |12. The cathode |10 of the selector tube |65 in the rst colorchannel is also connected to the grid |13 of a phase inverter tube |14in the rst color channel and to the cathode 2`|6 of selector electrontube 204 in the second color channel. The cathode |54 of the cathodefollower tube |45 is also connected through a resistor |15 to the grid|16 of a second selector tube |11. The grid |16 is also connectedthrough a resistor |18 to negative power input terminal |19. This gridbiasing network comprising the resistors |15 and |18 is connected to thecathode |54 of the cathode follower tube |45 in parallel to the gridbiasing resistors |63 and |66. The anode 488 of the second selector tube|11 is connected to positive power input terminal 489.

The anode of the phase inverter tube |14 is connected through a plateresistor |8| to positive power input terminal |82. The cathode |83 ofphase inverter tube |14 is connected through a cathode resistor |84 tonegative power input terminal |85. The anode |80 of the phase invertertube |14 is also connected through a resistance |86 to the control grid|81 of an electron tube |88. The grid |81 is also connected through aresistor |89 to a negative power input terminal |90. The anode |80 isalso connected through a resistor |9| to the control grid |92 of anelectron tube |93. The control grid |92 is also connected through aresistor |94 to negative power input terminal |95. The anode |96 of theelectron tube 88 is connected through a resistor |91 to the cathode |54of the input cathode follower tube |45 and is also connected to theanode 200 of an electron tube 20| in the third or lower color channel asviewed in Fig. 5. The anode |98 of the electron tube |93 is connectedthrough a resistor |99 to the cathode |55 of the input cathode followertube 46 in the middle channel as viewed in Fig. 5 and through a resistor202 to the grid 203 of the first selector tube 204 of the second colorchannel, the grid 203 being also connected through a resistor 205 tonegative power input terminal 206.

The cathodes 201 and 208 of the two electron tubes |88 and |93 areconnected to negative power input terminals 209 and 2|0, respectively.The cathode 2|| of the second selector tube |11 in the first or topcolor channel is connected to the grid 2|2 of the phase inverter tube2|3 in the third bottom color channel as viewed in Fig. 5 and is alsoconnected in parallel with the cathode 2| 4 of the second selector tube2|5 in said third or bottom color channel as viewed in Fig. 5, and isalso connected through cathode resistor 268 to negative power inputterminal 209 Referring to the middle color channel, the cathode |55 ofinput cathode follower tube |46 is connected through the resistance 202to a grid 203 of a selector tube 204. The grid 203 is also connectedthrough a resistor 205 to a negative power input terminal 206.

The cathode 2|6 of the first selector tube 204 is connected in parallelwith the cathode |10 of the rst selector tube |65 in the first or topcolor channel as viewed in Fig. 5 and is also connected through thecathode resistor |1| to negative power input terminal |12 and also tothe grid |13 of the phase inverter tube |14 in the top color channel.The anode 2|1 of the rst selector tube 204 of the middle color channelis connected to positive power input terminalZIll. The cathode |55 ofthe cathode follower tube |46 of the middle color channel is alsoconnected through a resistor 2I9 to the grid 226 of a second selectortube 22| or" the middle color channel. The grid 229 is also connectedthrough a resistor 222 to negative power input terminal 223. The gridbiasing resistors 2| 9 and 222 are connected to .the cathode |56I of thefollower |46, in lparallel to grid biasing resistors 292 and 295. Theanode 224 of second selector tube 22| is connected to positivepowerinput terminal 225. The cathode 226 of the second selector tube 22|is connected through a cathode resistance 221 to a negative power inputterminal 229. The control grid 229 of phase inverter tube 239 isconnected to the cathode 226 of the second selector tube 22! in themiddle color channel and also connected to the cathode 23| of the firstselector tube 232 in the third or bottom color channel as viewed in Fig.The anode 233 of the phase inverter tube A234 is connected through aplate resistor 234 to positive power input terminal 235. The anode 233ofthe phase inverter tube 236 is also connected in parallel to the gridbiasing circuits of two electron tubes 236 and 231. The anode `233isconnected through a resistor' 236 to the .control grid 239 of theelectron tube 236. The grid 239 is also connected through a resistor 246to negative power input terminal 24|. The anode 233 is also connected inparallel to the first mentioned grid biasing circuit through a resistor242 to the control grid 243 of the electron 'tube 231. The control grid243 is also connected through a resistor 4244 to `negative power inputterminal 245. rlhe cathode 246 of the phase inverter tube 236 isconnected through a cathode `resistor 241 to a negative power inputterminal.. 249. The anode 249 of the electron tube 236 is connected inparallel with the anode |98 of the electron tube H93 in the first colorchannel through the resistor |99 to the cathode i55 of the cathodefollower tube |46 of the middle vcolor channel and through cathoderesistor to negative power input terminal |6| and the grid biasingnetwork of tubes 294 and 22|. The cathode 486 of the electron tube 235is connected to negative power input terminal 431. The cathode 256 ofthe electron tube 231 is cone nected. to negative power input terminal25i. The anode 252 of the electron tube 231 is conn nected in parallelto the anode 253 oi an elec tron tube 254 in the third or bottom colorchannel as viewed in Fig. and through a resistor 3255 to the cathode |66of the cathode follower tube |41 in the third color channel and the gridbiasing network of tubes 2I5 and 232 and negative power input terminals62, 253 and 265.

Referring to the third or bottom color channel as viewed in Fig. 5, thecathode |56 of the input cathode follower tube |41 is connected througharesistor 256 to the grid 251 of a rst selector tube 232. The grid 251 isalso connected through'la resistor 258 to negative power input terminal259. The anode 260 of the first selector tube '232 is connected topositive power input terminal 26|. The cathode |56 of the input cathodefollower tube |41 is also connected in parallel to the grid biasingcircuit comprising resistors 256 and 258, through a resistor 262 to thegrid 263 'of the second selector tube 2 I5. The

control' grid 263 vis-also connected through a re sister 264 to anegative power Yinput terminal 265. The anode 266 of the second selectortube 2 I5 is connected Yto positive. power input termin'aI Pfr 261. Thecathode 2 I4 of the second selector 2I5 is connected through a cathoderesistor 268 to a negative power input terminal 269. The anode 213 ofthe phase inverter tube 2| 3 is connected through a -plate resistor 21|to a positive power input terminal 212. rihe anode 210 is also con-ynected in parallel to the grid biasing circuits of two electron tubes254 and 29|, saidyanode 219 being connected lthrough a resistor 599 tothe control grid 59| of the electron tube 254. The control grid 59| isalso connected through a resistor 213 to a negative power input terminal214. The anode 216 being also connected in parallel through a resistor215 to the control grid 2.16 of the pentode electron tube 20|; thecontrol grid 216 being connected through a resistor 211 to a negativepower terminal 218. The cathodei469 of `the phase inverter tube 2|3 isconnected through a cathode resistor 49| to negative power inputterminal 492. The cathode 219 of the electron tube 254 is connected to anegative power input terminal 299. The cathode 29| of the electron tube29| is connected to a negativeinput terminal 292. The anode 299 of theelectron tube 20| in the thirdl color channel yis connected in parallelwith the anode |96 of the electron tube |89 in the first oolor channelto a color output terminal 293 for the rst color channel. The anode |99of the electron tube |93 in the rst color channel is connected inparallel with the anode 249 of the electron tube 236 in the second colorchannel to a color output terminal. 234 for the second color channel.The anode 252 of the electron tube 231 in the second color channel isconnected in parallel with the anode 253 of the electron tube 254 inthethird color channel to a color output terminal 285 for the thirdcolor channel. Y

The operation of the color absorption corrector may be described asfollows: Input tubesv |45,

|46 and |41 are cathode follower tubes which have output voltagesvirtually the same as the input voltages to their grids |42, |43 and|44, and which have low output resistances. In order to give a specificillustration of the process, assume that the tubes |45, |46 and |41control the yellow, magenta and blue color channels, respectively. Tubes|65, 294, 232, |11, 22| and 2 I5 are selector tubes each of which isprovided at the input with a resistance network or volume control bymeans of which necessary adjustments can be made. The selector tubes areoperated in pairs corresponding to a vpair of colored inks. Tubes |65and 294 are the selector tubes which are used when the .yellow andmagenta inks are used together. If yellow ink is rst printed and magentaink is then superimposed thereupon by the halftone printing process, thesignal for Athe yellow is much less than its correct value and thesignal for the magenta is slightly less than its correct value. This canbe determined by calculating the color absorption characteristics of thetwo inks. Therefore, by the ,proper vchoice of resistances for theresistance networks at the inputs of tubes |65 and 294, conditions arexed so that common cathode voltage of these two selector tubes |65 and294 'is regulated by the least value of the two signals. An increase insignal or percentage coverage of ink corresponds to the primary inputvoltage or potential becoming more negative so the least value of thetwo signals mentioned above, corresponds to the more positive signal.The cathode 'voltage of the cathodes |19 and 2 I6 of the selector :tubes|65 and 294 is used as .the input .to the of the resistor phase invertertube |14, the output of which is, in turn, connected to the inputs oftubes |88 and |93. Tube |88 is connected to the yellow channel, theoutput terminal of which is 283. Tube |88 causes a voltage drop in theresistor |91 which results in an increase in signal and percent coverageof the corresponding colored ink. Likewise, the tube |93 causes anincrease in the magenta signal in order to give the correct value,although the required increase in signal is so small that it may beneglected and the tube |93 dispensed with.

It should be emphasized that these correction factors are not usedexcept when the two inks, yellow and magenta, are used together, becausethe correction factors are proportional to the least value of the signalor percentage coverage for the two inks. The conditions for the otherselector tubes and other combinations of colored inks are determined ina similar manner.

The three color output terminals 283, 284 and 285 are connected to leads59, and 52 as viewed in Fig. l and the black output from theantilogarithmic amplier 44 is connected to output lead 48. The fouroutput leads 59, 5|, 52 and 48 are connected respectively to four linearlight valves indicated generally at 53, 54, 55 and 56. These four lightlinear valves may be any type of linear light valve known in the art.For example, they may comprise mercury vapor rectier tubes used aslamps. Preferably such mercury vapor rectifier tubes should have heatediilaments but not necessarily so, in fact any type of light valveswherein the light output bears a linear relation to the electric inputmay be used. These four light valves are adapted to vary the intensityof light beams focused upon four photosensitive mediums locatedgenerally at 6 62, 63 and 64, such as photographic lm or the likemounted upon a drum indicated generally at 65 and adapted to be rotatedand axially advanced by vmeans. of any suitable driving mechanismindicated generally at 66. As hereinbefore mentioned, the fourth orblack antilogarithmic amplifier indicated generally at 44 may beutilized directly as an antilogarithmic nonlinear light valve in placeof the linear light valve indicated generally at 56 for making the blackseparation photographic negative 64 if so desired. Such a nonlinearantilogarithmic light valve is illustrated, described and claimed in mycopending application Serial No. 702,172.

It is to be understood that the three color channel leads 45, 45 and 41coming from the antilogarithmic amplifiers 4|, 42 and 43 may berespectively connected directly to the upper ends |63 in the first colorchannel shown in Fig. 5, the upper end of the resistor 292 in the secondcolor channel shown in Fig. 5, and the upper end of the resistor 255 inthe third color channel shown in Fig. 5. In other words, the ink colorcorrector input terminals |39, and |4|' and the input cathode followertubes |45, |46 and |41, may be dispensed with entirely, and, ashereinbefore explained, the input connected directly to the three leadsshown connected to cathodes |54, |55 and |58 of the three cathodefollower input tubes |45, and |41 shown in Fig. 5.

It is to be understood that the system shown diagrammatically in Fig. 1may be operated, if desired, without the color absorption correctorshown generally at 49.

The output of each of the three differential logarithmic ampliers 23, 26and 29 may be sent to a suitable transmitter (in the event thephotographic separation images are to be made at a considerable distancefrom the place of origin). Suitable receiver means may be connected tothe input leads of the additive or subtractive mixer 36 for receivingthe transmitted color channel signals if so desired.

It is understood, of course, that the system shown diagrammatically inFig. l, is of the type referred to hereinabove wherein each colorchannel is provided with two receptors, the spectralsensitiVity-versus-wave length response of one photographie receptorbeing subtracted electrically, photographically or otherwise from thespectral response of the other photographic receptor, thus, making acombined receptor for each color channel having a spectral response,positive in certain spectral regions and negative in other spectralregions; said combined spectral response or sensitivity being determinedby the three colored inks to be used in reproduction. This isillustrated in Figs. l1l 12 and 13, where the curve shown in Fig. 1l isthe desired cornbined spectral response, and the curves shown in Figs.l2 and 13 are curves obtainable with practical receptors which whencombined by subtracting the curve shown in Fig. 13 from the curve shownin Fig. 12 virtually equal the desired curve shown in Fig. l1.

A second diagrammatic representation of various elements combined into asystem for making three correct color separation negatives and a blackseparation negative from three color separation positives is shown inFig. 2. Generally speaking, the system shown diagrammatically in Fig. 2comprises a scanning drum indicated generally at upon which are mountedthree color separation photographic positives 286, 281 and 288. The drumis adapted to be rotated and axially advanced by suitable drivingmechanism indicated generally at 8. Details of construction of thescanning drum and driving means need not be illustrated since such meansare available and known in the art. Positioned within the scanning drumare photoelectric cells 289, 290 and 29| adapted to receive light fromsources 292, 293 and 294, respectively.

The photoelectric cells 289, 290 and 29| are connected as by lines 295,296 and 291, respectively, with a color transformer indicated generallyat 298. Leads 295, 296 and 291 constitute portions oi three separateimaginary primary color channels to which reference will be madehereinafter.

It should be noted at this point that the three photographic colorseparation positives 295, 261 and 288 have been made through suitablefilters such that the spectral response of each receptor comprising thephotographic positive, the filter through which the image has been made,and the photoelectric cell which scans the positive, is such that theoutput of each imaginary primary color channel delivered to the colortransformer through leads 295, 295 and 291 is related to the lightoriginally emitted, reflected or transmitted by the colored subject soas to virtually correspond to a select spectral sensitivity versus wavelength curve corresponding to imaginary primary reproducing colors.

Such spectral response curves are shown in Fig. 9, for imaginary primaryreproducing colors as shown on chromacity diagram shown in Fig. 10. Thischromacity diagram has been calculated from data given in HardysHandbook of Colorimetry. The vertical coordinate is y and the noone-"horiliontal; cdrdinate.y is: a1. The coordinate afi's not.. shown.`onathev diagram, but'. it; may be iou'ndf. from; the. equation,r-lfvy.}.z=1.. The coordinates;

of. thethree imaginary reproducing colors are as follows.:

Firstprimary. v v ='1,.y.=0, 2:0 Second,primary l v ;r=0, 11:1, 2:0.Thirdprimary 32:0, y=0fz:.=1`

Asn hereinbefore explained,v using imaginary primarycolors at the inputendof the apparatus-- essboth positive. and" negative values of'spectral;

response foreach' color channel are automatically'compensatedfor. Thedetails. of onepreferred` form. of the' color transformer areillustrated" schematically in Fig. 7 and Will be discussed hereinafter.

Referring to Fig. 2, real primary output.. leads 299';Y 3.0.0 and30 llfrom the color transformer 232i arei connected to the input'of amultiplying Vmixer indicated" generally at 302. The function of themixer-3024s similar to the combined functions of the differentiallogarithmicV amplifiers; additive or subtractiven mixer, andantilogarithmic ampli.-

ers;shown-in Fig; 1 illustrating' the rst' form of my invention, in thatthev multiplying or dividingv mixer 5m2-y actsso as tosimilarlyvmultiply the signalsinjalllthreeof the colorsignals so as tocause the instantaneous signal in one oftheicol'or channels whichlcorresponds to the least colored ink coverageI for that channel, to bemaintained at a value'corresponding to noA coloredfink coverageY forthatchannel, the signals' in the other twoV channelsF being multipliedYequally. rThis; is an equal'V multiplying action of all three or theVsignais-vin" the various colorchannels;

mixerl 3-02' takes three' input. signalsin three color channels andmodies them into three output.

signals in three color4 channels and ablack out# putsignal;

Ashereinbefore explained; thisdirect multiplying action ismathematicallythe-same' as that achieved in the'rst form of -niyinvention. illustratedin Fig; 1 Where logarithme are first taken,

thenaddition tov orsubtracton from logarithms:

i's'accomplished lfor modifying threecolor channel`v input signals intothree color channel out put4 signals and a-bla'ck color' channeloutputsig nal, andthe antilogarithm of the outputsigrnals` is-ta'ken.E

Details' of the preferred form of multiplyingmixer-aref illustrated inFig; 6 and will' be described hereinafter.

'Ihe three color channel outputsv which haveV been, modied by.` themultiplying Vmixer arecon-r nectedtol input leads` |45, |46, and |41 ofthe ink color absorption corrector indicated generallyv at 1 49.'The'inkgcolor absorptioncorrector 49 is-the same-as that show-n inFig.land hereinbefore described andillustratedin Fig; A5.

Y Thef-threecolor 'channel'.output leads 50, 5 I` and' 52: from the;superimposed; ink: color. absorption.

The` amount'V of'saidv multiplication is then used as the black outputsignal; in other words; the multiplying,

corrector 49H are connected to. linearl light: valves'v indicatedlgenerally Vat 53;.54 .and 5.5. Theblack. outputchannel fromthe-multiplying; mixer 332' is. connected; through:h the input lead. 452to the. anti,-v logarithmic ampliiier 44', Whose outputichannel;

carriesstheblack. output signal.` The reason. for.thisisthatthemultiplying factor by-Which all of the colori-signals: in`the.` three color channels |45, |46, and-: l''thave: been multiplied bythemultiplyingizmixer V3h21 bears a' logarithmic .relation to themaximum. signal. with. respect to` light. in the threei color channels:V2919., 380:; and 30|, and itis desired.` thats theI actual. black.Voutput signal be proportionalstothat maximumasignal. Thisishecausefofathe characteristics of thefelectron multi plier.v photoztubes2.89; 295i andY 29| the amplication factors of; which are controlledbythe multiplying mixen .'llhiswillbe explained ingreater detailiin thespecific; descriptionof thermlltiply-` ing; mixer given hereinafter.

The antilogarithmic -ampliiier 44 modifies the black; inputsignal@sothatv the black.` output signal is virtually..antilogarithmiclwith. respect to said black: imputa. signal. Said black output signal 1,passesfthroughblack.signal lead 48K to blackflinear light valve.-indicated .generally at-` 56. As. herein-` beforef. explained, ratherthan` connect the black antilogarithmic amplifier 44'. to the-.blacklinear light: valve-5'0";kv the antilogarithmic ampliiier 44- may beused, directly as a nonlinear antilogarithmicv lightvalye and the linearlight Valve 56 may bel omitted entirely` if so-desired. The antilogarithmictamplifier 44. used either as an antilogarithmic amplifier or`asl an antilogarithmic light valve islet the-type illustrated,described andvl claimed; i nimy. copendlng; application.

The: three colorrchannel linear light valves' 53, and iisandythe black:linear light valve' Stare adaptedtoivaryi the lightifrom-sources 51, 58,59 and l'iwhich'. is focused: upon-zfour photosensitiveA mediums.such'as...photographic lms, orithe like, indicated. at 61:, 62,. 63. andv54.v The films 6|, 62,

6.3'. and; 642 are-l mounted: upona drum 65 which isvadapted?toxbelrotated;andy axially advanced by drivingfmechanismindicated. generally at 65 and.v Whichiis old inftheiartandfwill not bedescribedr herein'.

Although in vthe system'shoWndiagrammatical-- ly-inFig; 2; .the'colortransformer.v is shown'- placed after. thee threey photocells; andbefore themulti-v plying.,mi'xer, inactuality.` the photocells arewpartofithegmultplying. mixer, and the photocells and thee multiplying: mixershunt the color transformen'and are connected: to both input and outy.pntiterminalsthereofi In other Words, the input. terminal'szof the colortransformer 298 are connected tcrthe'outputlterminals oflthe threephoto-- cells; 2189.,.112'90, 291|,.and; the outputterminals off the;colorztransfrmer `298 are; connectedv to theinputlt'erminals ofthemultiplying mixer 302, and the lnultiplyingmixen 3.5.2 isalso connectedback to` theyphotoeells 2393.395 and 29H in an inverse feedback-i mannenfor varyineu the ampliiieation. thereof Therefore, the/three photocellsand the: multiplying. mixer., will be describedl in detail first rathertliarrtlie.color transformer which is shown. irstv diagrammaticallyinFig. 2;

Multipli/ing mixer Schematic drawing off the multiplying mixer is shownin Fig. 6. Referring to said'gure, the

tlireeelectron multiplying phototubes indicated generally.K at 2891,'.29'0 and 29| arethe scanning; photocell's adapted to scan photographiccolor separation positives 286. v281 and 288 shown in Fig;

23 2. The electron multiplier phototubes 289, 290 and 291 may be of atype well known in the art, such as the RCA 931 electron multiplierphototube, or any other suitable tube. Said tube is anelectro-statically focused electron multiplier phototube. The tappedresistors or voltage dividers 303, 304 and 305 are connectedrespectively across the plurality of electrodes known as dynodes and thecathodes 306, 301 and 308 of the electron multiplier phototubes 289, 290and 291. The cathodes 306, 301 and 308 of the Phototubes 209, 290 and29| and the lower ends of the tapped resistors 303, 304 and 305,respectively, are connected in parallel to the anode 309 of an amplifiertube 3 I 0 and also to the black channel output terminal 3| I. The upperor last dynode of the electron multiplier phototubes 289, 290 and 291and the upper ends of the tapped resistors 303, 304 and 305 areconnected in parallel to positive power input terminal 312. The anodes313, 314 and 315 of the electron multiplier phototubes 289, 290 and 291are connected to phototube output terminals 316, 311 and 318 and thenthrough plate resistors 319, 320 and 321 to positive power inputterminals 322, 323 and 324, respectively. The output terminals 316, 311and 318 are adapted to be connected to the input terminals of the colortransformer 298 shown in Figs. 2 and 1. The output terminals of thecolor transformer 298 shown in Figs. 2 and 'I are adapted to beconnected to input terminals 325, 326 and 321 of the multiplying mixershown diagrammatically at 302 in Fig. 2 and in detail in Fig. 6. Theinput terminals 325, 326 and 321 of the multiplying mixer are connectedto the grids 328, 329 and 330 of electron tubes 331, 332 and 333,respectively. The input terminals 325, 326 and 321 are also the outputterminals of both the mixer and the color transformer and are adaptedyto bevconnected to the input terminals of the ink color absorptioncorrector shown generally' at 49 in Fig. 2 and in detail in Fig. 5. Theanodes 334, 335 and 336 of the electron tubes 331, 332 and 333 areconnected to positive power input terminals 331, 338 and 339,respectively.. The cathodes 340, 341 and 342 of the electron tubes 331,332 and 333 are connected in parallel through a resistor 343 .tonegative power input terminal 344. Said three cathodes are alsoconnected in parallel through a resistor 345 to the grid 346 of anamplifier tube 341. The grid 346 is also connected through a resistor348 to negative power input terminal 349. The anode 350 of the amplifiertube 341 is connected through a plate resistor 351 to positive powerinput terminal 352. The anode 350 of the amplifier tube 341 isresistively coupled to the grid 353 of the amplifier tube 310 by meansof resistors 354 and 355. Resistor 355 is connected to negative powerinput terminal 356. The cathodes 351 and 358 of the amplifier tubes 310and.

341 are connected in parallel to negative power input terminal 359.Tubes 331, 332 and 333 have a rectifier action in that the most positivegrid of the three tubes determines the voltage of the three cathodes340, 341 and 342 which are connected together. Tubes 341 and 310 areamplifier tubes and are used so that a very small voltage change of thecathodes 340, 341 and 342 will produce a large change in voltage acrossthe tapped resistors 303, 304 and 305 across the dynodes 'of theelectron multiplier photocells 289, 290 and 291 and thus, produce a verylarge change in the amplification or sensitivity in each of the threephotocells, This system operates in an inverse feedback manner.

It can be seen `that the amplification of each' of the three photocellsis equally changed by the multiplying mixer so that the three coloroutput signals at terminals 325, 326 and 321 are such that the voltageof the one of the output terminals which corresponds to the leastcolored ink coverage of that channel is maintained at a' valuecorresponding to no colored ink coverage for that channel and the othertwo channels are similarly multiplied. The color transformer is adaptedto be positioned between the three photocells 269, 290 and 291 and therectier tubes.

331, 332 and 333.

Color transformer Fig. 7 illustrates in detail the color trans-v formerindicated generally at 298 in Fig. 2. The

three color channel input terminals to the colorv transformer are 361,362 and 363. Said input terminals 361, 362 and 363 are connected to thegrids 364, 365 and 366 of cathode follower tubes 361, 368 and 369,respectively. The anodes 310,

311 and 312 of the cathode follower tubes 361,I

369 and 369 are connected to positive power input terminals 313, 314 and315, respectively. The cathodes 316, 311 and 318 of the cathode followertubes 361, 368 and 369 are respectively connected through cathoderesistors 319, 380 and 381 to negative power input terminals 382, 383and 384. The cathode 316 of the cathode -follower tube 361 is alsoconnected to the grid 335.l

of a phase inverter tube 386, The cathode 311:' of the input cathodefollower tube 361 of the first 0r upper color channel is connected tothe grid, ,365 of the phase inverter tube 386. The anode 408 of thephase inverter tube 386 in the first color channel is connected throughplate resistor 4.69 to a positive power input terminal 410. The anode408 is also connected through a resistor 411 to the control grid 412 ofthe cathode follower tube 406 of the first color channel. The controlgrid 412 is also connected through a resistor 413 to negative powerinput terminal 414. The cathode 415 of the phase inverter tube 386 isconnected through a resistor 416 to a negativev power input terminal411. The anode 418 of the cathode follower output tube 406 of the rstcolor,

channel is connected to positive power input terminal 419. The cathode405 of the output cathode follower tube 406 is connected through acathode resistor 421 to a negative power input. The cathode 405 of theoutput.

terminal 422. cathode follower tube 406 of the first color channel isalso connected through resistor 404 to the output terminal 401.

The cathode 311 of the input cathode follower tube 368 of the second ormiddle color channel is connected to the grid 390 of the phase invertertube 391. tube 391 in the second color channel is connected through aplate resistor 425 to positive power input terminal 426. The anode 424is also con--A nected through a resistor 421 to the control grid 428 ofthe output cathode follower tube 399 of the second color channel. Thecontrol grid 428 is also connected through a resistor 429 to 4negar tivepower input terminal 430. The cathode 431 of the phase inverter tube 391is connected through a cathode resistor 432 to a negative power inputterminal 433. The anode 434 of they output cathode follower tube 399 isconnected to a positive power input terminal 435. 'Ihe catliode 398 ofthe output cathode follower tube 399l of the second color channel isconnected through a cathode resistor 436 to negative power input" Theanode 424 of the phase inverter' terminal 431. The cathode 398 of theoutput cathode follower tube 399 is connected to output terminal 433through resistance 391. The cathode 318 of the input cathode followertube 369 of the third or lower color channel is connected to grid 40| ofthe phase inverter tube 402. The anode 439 of the phase inverter tube40.2 is connested through a plate resistor 440 to positive power inputterminal 44|. The anode 439 is also connected through a resistor 442 tothe control grid 443 of the output cathode follower tube 394 of thethird color channel. The control grid 443 is also connected through aresistor 444 to negative power input terminal 445. The cathode 446 ofthe phase inverter tube 462 is connected through a cathode resistor 441to a negative power input terminal 448. The anode 449 of the outputcathode follower tube 394 of the third color channel is connected topositive power input terminal 450. The cathode 393 of the output cathodefollower tube 394 of the third color channel is connected through acathode resistor 452 to negative-power input terminal 453. The cathode393 of the output cathode follower tube 394 is also connected to outputterminal 395 through resistance 392. The three color channels areinterconnected by means of the following resistances so that a part ofthe signal in each color channel can be subtracted from the signal ineach of the other two color channels. Cathode 316 of the input cathodefollower tube 361 of the first color channel is connect-ed throughresistance 381 to output terminal 395 of the third color channel and isalso connected through resistance 396 to the output terminal 436 of thesecond color channel. Cathode 311 of the input cathode follower tube 368of the second color channel is connected through resistance 389 tooutput terminal 395 of the third or lower color channel and is alsoconnected through resistance 423 to the output terminal 401 of the firstcolor channel. Cathode 318 of the input cathode follower tube 369 of thethird or lower color channel is connected through resistance 493 to theoutput terminal 491 of the first color channel and is also connectedthrough resistance 460 to the output terminal 438 of the second colorchannel.

The three color channel output terminals 401, 438 and 395 are adapted tobe connected to the terminals 325, 326 and 321 of the multiplying mixershown in Fig. 6. The input terminals 36|, 362 and 363 of the colortransformer as shown in Fig. 1 are adapted to be connected to the outputterminals 3 i6, 3 1 and 3 8 of the three photocells 389, 390 and 39|shown in Fig. 6. The input voltagesat the input terminals of the colortransformers 36|, 362 and 363 vary the bias on the grids 364, 365 and356 of the cathode follower tubes 361, 368, and 369 and cause thevoltages of the three cathodes 316, 311 and 318 to follow said gridvoltages closely.

The reason for the use of the cathode follower tubes 361, 369, 369, 406,399 and 394 is the small incremental resistance to ground obtainedthrough the use of said tubes. The resistances 494, 391, 392, 423, 463,396, 406, 381 and 389 are all large in comparison lto the incrementalresistance between each of the cathodes of the cathode follower tubes361, 368, 369, 496, 399 and 394, and ground. This makes the voltages ofthe cathodes of these cathode follower tubes practically independent ofthe currents through resistances, 494, 391, 392, 423, 403, 396, 400, 331and 389. This is done in order to insure that the three output circuitsdo not interfere with each other. circuits is formed by the resistances404, 423 and 463. Another of these output circuits is formed by theresistances 391, 396 and 400. The third output circuit is formed by theresistances 392, 389 and 400.

Tubes 386, 39| and 492 are phase inverter tubes. The cathode resistanceof each is so chosen as to produce, as nearly as practicable, a linearrelation between plate voltage and grid voltage. Tubes 486, 399 and 394are output cathode follower tubes connected to the output of the phaseinverter tubes 386, 39| and 492. The voltages from the cathode followertubes 406, 399 and 394 are combined by means of the resistances shown.The output voltages of the resistance network which are fed to theoutput terminals 491, 438 and 395 correspond to the real primary colorchan-k nel output voltages.

It should be mentioned here that photographic positives are beingscanned and that the resistances in the resistance network areproportioned so as to give the greatest weight to the voltages from theoutput cathode follower tubes. Thus the primary voltage corresponding tothe most light from the picture being reproduced is also the mostpositive.

It is the function of the color transformer to subtract from the signalin each color channel a portion of the signal in each of the colorchannels. For each color channel the change in voltage of the cathodesof the output'cathode follower tubes is opposite in sign to the changein voltage of the cathode of the input cathode follower tube. The outputcathode follower tube represents positive values of the signal and theinput cathode follower tube represents negative values of the signal. Bythe use of the proper resistances the voltage at each output terminalrepresents the main portion of the signal from one color channel minus aportion of the signal from each of the other two color channels. Thislinear recombination of signals is for the purpose of converting theinput color signals, which represent the values for imaginaryreproducing primary colors, into output color signals which representthe values for real reproducing primary colors. More specifically, thesereal reproducing primary colors are the complements of the colors of thecorresponding reproducing inks.

' The relationships between the output signals and the input signals ofthe color transformer are calculated by means of the principles ofcolorimetry as set forth hereinbefore.

Fig. 3 illustrates diagrammatically another general arrangement ofvarious elements which may be utilized in making three correct colorseparation negatives and a correct black separation negative from sixcolor separation positives, two positives to each of three colorchannels. This system is of the type for which the one positive of eachcolor channel has a spectral sensitivity-versus-wave length curvepositive in certain spectral regions and the other photographic positiveof that color channel having a spectral sensitivity-versus-wave lengthcurve positive in another and different spectral region.

, Referring to said Fig. 3: A scanning drum indicated generally atrequiring six color separation positives 2, 3, 4, 5, 6 and 1, is rotatedand axially moved by a suitable drive generally indicated at 0.Positioned within the scanning drum are photocells 9, I6, |2, I3 and I4adapted to receive light from sources l5, I6, |1, |8, I9 and To be morespecific, one of these output Y respectively. The pliotoelectric cellsil and lll fare'connected as by leads 2| and 22 to the difierentialmultiplying mixer indicated generally at 360; Fhotoelectric cells and l2are connected asrby leads 24 and 25 to the differential multiplyingmixer 366. Photoeleotric cells |3 and |4 are connected as by leads 21and 28 to the differential multiplying mixer 360. The leads 2| and 22constitute a portion of one color channel. and 25' constitute a portionof a second color channel and the leads 21 and 28 constitute a portionof a third color channel.

In general, the scanning drum and drive, photographic positives, sourcesof light, scanning photocells, and the six leads comprising threecolorchannels with the two leads of each channel going to thedifferential multiplying mixer 360', are the same asthe similar elementsin the first form of my invention shown in Fig. l.

As shown in Fig. 3 the photocells operate in pairs as in the case of thedifferential logarithmic amplifiers previously described and showndiagrammatically in Fig; 1. Subtraction ofthe signal of one photocellfromy the signal of the second photocell of each pair is carried out inthe same manner as'shown for the differential amplifier, more completelydescribed in my Patent No. 2,454,871. Means for this subtraction arevnot shown in Fig. 3.' From each pair of photocells, then, there isproduced a signal corresponding to a real reproducing primary color. Bythe proper choice of the color lters for making the positives 2, 3, 4,5, 6 and 1, the three signals thus produced correspond exactly to theoutput signals from the color transformer 302 of Fig. 2. The three colorsignals thus produced are fed to the three input terminals of themultiplying mixer shown as 560 in Fig. 8 and also shown in Fig. 6. Thecathodes of all six multiplier photocells shown in Fig. '3 are connectedtogether and to the plate 369 of the tube 3|@ shown in Fig. 6. As shownin Fig. 6, the plate 36S of tube 3|0 is also connected to terminal 3||.This is the black output terminal of--the multiplier mixer andcorresponds to line 4D of Fig. 3.

In the above manner the multiplying factors for all of the scanning`phototubes are made equal.- The net result is that the multiplyingfactor for each of the three color channels is equal and .is controlledby the multiplying mixer so that the color signal corresponding to themaximum coverage of ink is regulated to a value correspondingessentially to Zero coverage of ink.

The three color channel outputs from the differential multiplying mixer356 are connected to input leads 45, 46 and 41 of the ink colorabsorption corrector indicated generally at 49'. The superimposed inkcolor absorption corrector 49 is the same as that indicated generally inFigs. 1 and 2 also and more specifically in Fig. 5 and hereinbeforedescribed.

The black output channel from the differential multiplying mixer 365 isconnected to the input lead. of the antilogarithmic amplifier 44 in amanner similar to that shown in Fig. 2. The antilogarithmic amplier 44is not herein described since it is illustrated, described, and claimedin my copending application, Serial No. 702,172.

The black output lead 4B of the antilogarithmic amplifier 44 isconnected to black linear light valve indicated generally at 56. Ashereinbefore mentioned, the black linear light valve 56"may be dispensedwith entirely and the anti.-

Leads 24 28 logarithmic amplifier 44 used as an antiloga# rithmicnonlinear light valve as described in my copending application.

The color channel output leads'56, 5| and 52 of the ink color absorptioncorrector 49 are con# nected to linear light valves 53, 54 and 55. Thefour linear light valves 53, 54, 55 and 56 are adapted to vary the lightfrom light sources 51, 5S, 59 and 66, which is focused uponphotosensiftive mediums such as four photographic filaments 6|, 62, 63and 64 or the like, which are mounted upon a drum indicated generally at65 and which is adapted to be rotated and axially moved by a suitabledrive indicated generally In general, the input portion of the systemshown diagrammatically in Fig. 3 is much like the input portion of thesystem shown diagrammatically in Fig. l and the output portion of thesystem shown diagrammatically in Fig. 3 yis much like the output portionof the system shown diagrammatically in Fig. 2.

Compensator Fig. 8 illustrates what I have called a com'- pensator. Thiscompensator may combine the functions of color transformer of myinvention shown diagrammatically in Fig. Zand in detail in Fig. 7 anddescribed hereinbefore, and the function of the ink color absorptioncorrector of my invention shown diagrammatically in Figs.V

l, 2 and 3 and in detail in Fig. 5 and described hereinbefore.

The compensator may act as either a color transformer or an ink colorabsorption corrector or both if so desired. It may also be used as willhereinafter be explained in systems for making a colored reproduction orfacsimile by spraying ink upon a suitable medium such as paperI or thelike. It may be used with linear or logarithmic output.

Referring to Fig. 8, the compensator is pro# vided with three colorchannel input terminals 454, 455 and 456. The first color channel inputterminal' 454 is connected to similar deilecting plates 451, 456 and 459of three cathode ray tubes indicated generally at 460, 46| and 462. Thesecond color channel input terminal 455 is connected to similardeflection plates 463, 464 and 465'of the cathode ray tubes 460, 46| and462 respectively. The third color channel input terminal 455 isconnected to similar deflection plates 466, 461 and 468 of the cathoderay tubes 460, 46| and 462. The three color channel input terminals 454,455 and 456 may be connected directlyA to the output terminals 325,326and 321 of the mixer shown in Fig. 6. In such case the photocell outputterminals 3| 6, 3|1 and 3|8 may be connected to the grids 325, 326,and321, respectively of the three rectifier or selector tubes of themixerdirectly or through cathode follower tubes with corresponding circuitchanges.

Positioned opposite the ends of the cathode ray tubes`466, 46| and 462,the inner sides of which.

are coated with'a material capable of fluorescing" under the influenceof the electron beam impinging thereon, are three electron multiplierphototubes indicated generally at 469, 410 and 41|. These electronmultiplier phototubes have tapped resistors or voltage dividers 412, 413and 414 across the dynodes of said phototubes, the lower end of eachresistor being connected to the photo cathodes 415, 416 and 411 of thephototubes 469,

416 and 41|, respectively. The lower ends of thethree tapped resistors412, 413 and 414 and the

